Winding layers composed of different materials

ABSTRACT

Fewer insulation layers can be used by virtue of using hydrophobic electrically conductive materials around a main insulation around a conductive bar. There are several more layers of conductive and/or non-conductive material.

The invention relates to winding layers composed of different materials.

Potential control makes it possible in rotating machines, such as forexample generators or high-voltage motors, to minimize electricalvoltages (potential differences), thereby allowing the occurrence ofpartial and/or corona discharges to be reduced or avoided entirely.

In rotating electrical machines, the reliability of the insulatingsystem is decisively responsible for their operational reliability. Theinsulating system has the task of permanently insulating electricalconductors (wires, coils, bars) from one another and from the laminatedstator core or the surroundings. Outer potential control has the task ofmaking electrical contact between the laminated stator core at groundpotential and the outer side of the main insulation. This ensures thatno partial discharges occur in voids in the region of the boundary layerof the insulation and the laminated core.

A distinction must be made here between

-   -   outer corona protection (OCP) for generator winding bars that        have been produced by single bar production (OCP-S) and    -   outer corona protection (OCP) for generator winding bars that        have been produced by means of the GVPI process (OCP-G).

In the case of globally impregnated stator windings (Global VacuumPressure Impregnation GVPI), the entire laminated core with a fullyfitted winding is impregnated and cured altogether. As a result, theadhesive bonding of the winding in the slots of the laminated core is sostrong that the different coefficients of expansion of the copper, ironand insulation lead to high thermomechanical stresses between thecopper, insulation and iron, which after a certain number of thermalcycles (starts and stops of the generator) may lead to tearing open ofthe boundary surfaces. In order to prevent the gaps from being subjectto a difference in electrical potential, and the partial dischargesigniting there from destroying the insulation, an outer potentialcontrol (outer corona protection, OCP) is used, represented in FIG. 20as a double-layered outer corona protection, such as is used for thepotential control of machines processed by means of G-VPI.

An insulating base winding 70 of fine-mica tape is applied over thecurrent-carrying Roebel bar of copper conductor elements 40, smoothingand increasing the edge radii of the thin copper conductor elements 40.

Wound thereover is a first graphite-containing conductive nonwoven tape100, which is only connected at one point to the high-voltage potentialof the copper conductor element 40 by way of a contact strip 130.

It is only thereupon that the main insulation 160 of fine-mica glass iswound. Instead of the copper conductor elements, the first conductivenonwoven tape 100 thus forms the high-voltage electrode. It ispermanently adhesively bonded to the main insulation.

Following on top of the main insulation 160 is the inner outer coronaprotection winding 110 according to the prior art, an outermostseparating tape 190′ and an outer outer corona protection winding 200.An outer corona protection tape 140, which is woven in the outermostseparating tape 190′, connects the inner outer corona protection winding110 and the outer outer corona protection winding 200.

The thermomechanical stresses occurring between the copper conductorassembly and the insulation during the starting and stopping of thegenerator may after a certain operating time lead to local detachmentsof the insulating sheath from the conductor, without the feared partialdischarges igniting in the gaps that are produced. The region of thedelamination is potential-free, because the high-voltage potential hasbeen transferred to the conductive nonwoven that becomes baked fast onthe main insulation. This IPC design at the highly stressed innerboundary layer between the conductor and the insulation allowsturbogenerators to be operated at peak load for decades without anynotable partial discharge aging.

The object of the invention is therefore to solve the aforementionedproblems.

The object is achieved by an insulation system according to claim 1 foran OCP-S, an outer corona protection according to claim 17 and anelectrical machine according to claim 18.

Further advantageous measures that can be combined as desired with oneanother in order to achieve further advantages are listed in thesubclaims.

In the figures:

FIGS. 1 to 19 show various windings,

FIG. 20 shows an outer corona protection.

The figures and the description only represent exemplary embodiments ofthe invention.

FIG. 1 shows an insulation 1′ around a metallic bar 4, which has a maininsulation 7 (not represented any more specifically), including innerpotential control (IPC) around the metallic bar 4 (or metallicmaterial).

The main insulation 7 has preferably been applied directly to themetallic bar 4 (FIGS. 1, 2 and 3).

The main insulation 7 is preferably wound and preferably comprises micaor some other known material for the insulation.

On the main insulation 7 there is a further layer 10 of a well-adhering,electrically conductive material (preferably from the Krempel company)of the prior art.

Wound up on this layer 10 is an electrically conductive, hydrophobictape 11′ as the layer 12′, the tapes 11′ overlapping.

The material of the tape 11′ therefore differs significantly from thematerials of the layers 7, 10 and 13.

On this layer 12′ there is in turn a well-adhering, conductive windingtape for the formation of the outermost layer 13 (FIGS. 1, 2 and 3),which may comprise the same material as the layer 10.

As a difference from FIG. 1, depicted in FIG. 2 is a further variant 1″of the insulation system, in which the tapes 11′ abut one another, i.e.do not overlap in the layer 12″ thus formed.

The materials for the layer 12″ are preferably identical to the layer12′.

Shown in FIG. 3 is a further variant 1′″ of the insulation system, inwhich, on the basis of FIG. 2, the tapes 11′ have a clearance or spacing15′ between one another and form the layer 12′″.

The materials of the layers 12″ and 12′″ are preferably identical.

Shown in FIG. 4 is a further insulation 1 ^(IV), in which there isaround the metallic bar 4 a main insulation 7 with an adhering,electrically conductive material and a further layer 10 a tape 11′ in anoverlapping manner in the layer 12′ or only abutting (FIG. 5, layer 12″,insulation 1 ^(V)) or with a clearance 15′ in between (FIG. 6, layer12′″, insulation) This corresponds to the exemplary embodimentsaccording to FIGS. 1 to 3 without the outer layer 13, i.e. theelectrically conductive, hydrophobic material (layer 12′, 12″, 12′″)forms the outermost layer.

The main insulation 7 has preferably been applied directly to themetallic bar 4 (FIGS. 4, 5 and 6).

In FIG. 7, a further variant of an insulation 1 ^(VII) is shown. Themain insulation 7 has preferably been applied directly to the metallicbar 4.

In the case of this variant 1 ^(VII), directly on the main insulation 7there is electrically conductive, hydrophobic material of the tape 11′,which forms the layer 12′, 12″ or 12′″, around which there is awell-adhering, electrically conductive and preferably outermost layer13. This corresponds to FIGS. 1, 2 and 3 without the intermediate layer10.

FIGS. 8 to 10 show further variants of the insulation system 1 ^(VIII)to 1 ^(X).

The main insulation 7 has preferably been applied directly to themetallic bar 4 (FIGS. 8, 9 and 10) and similarly the layer 13 ispreferably the outermost layer (FIGS. 8, 9 and 10).

The starting point in the case of FIGS. 8, 9 and 10 is in each case ametallic bar 4, on which there is a main insulation 7 and awell-adhering, electrically conductive material directly thereupon asthe layer 10.

Arranged in an overlapping manner on this layer 10 there is according toFIG. 8 in a layer 12 ^(IV) both a tape 11 ^(III) of well-adhering,electrically conductive material and a tape 11″ (corresponds to tape 11′(FIGS. 1-7)) of an electrically conductive, hydrophobic material. Thetapes 11″, 11′″ overlap.

According to the embodiments of layer 12″ in FIG. 9, on the basis ofFIG. 8, the edges of the two different tapes 11″, 11′″ abut one another.

The two tapes (11″, 11′″) may form one tape, i.e. they have a left-handedge as one half of electrically conductive, well-adhering material anda right-hand edge as the other half of an electrically conductive,hydrophobic material.

Similarly, the two tapes 11″, 11′″ with the different materials may bearranged at a spacing 15″ from one another (FIG. 10).

In FIGS. 11, 12 and 13, further variants of an insulation system 1 ^(XI)to 1 ^(XIII) are represented.

The main insulation 7 has preferably been applied directly to themetallic bar 4.

On the basis of FIGS. 8 to 10, here it is just that there is no outerlayer 13, i.e. the electrically conductive, hydrophobic material (11″, .. . ) forms the outermost layer.

The materials are preferably identical to those of FIGS. 8-10.

Shown in FIG. 14 is a further variant of an insulation system 1 ^(XIV),two tapes 11″, 11′″ respectively of well-adhering, conductive material11′″ and electrically conductive, hydrophobic material 11″ being woundup in an overlapping manner on the main insulation 7.

As the outermost layer 13, there is a material of a well-adhering,conductive material.

In the variant 1 ^(XV) according to FIG. 15, the various tapes 11′″, 11″are present, abutting one another with their edges or with a clearance15″ between one another (FIG. 16).

FIGS. 14 to 16 respectively correspond to FIGS. 11 to 13, without theinsulation 10 on the main insulation 7, but with an outer layer 13, i.e.the electrically conductive, hydrophobic material does not form theoutermost layer.

The main insulation 7 has preferably been applied directly to themetallic bar 4 (FIGS. 14, 15 and 16).

FIGS. 17, 18 and 19 show further variants 1 ^(XVII) to 1 ^(XIX), inwhich, on the basis of FIGS. 14 to 16, there is no outer material 13 ofa well-adhering, conductive material, i.e. the electrically conductive,hydrophobic material forms the outermost layer.

The materials are preferably identical.

The main insulation 7 has preferably been applied directly to themetallic bar 4 (FIGS. 17, 18 and 19).

The selection of the number of layers 10, 12, 13 or the addition of theoutermost layer 13 and/or an inner layer 10 with a material of the priorart depends on the area of use of the insulation, to be specific on thevoltage used (more layers) and on the outer surroundings (outermostlayer).

The invention comprises using hydrophobic material, in particular PTFE(Teflon) for the insulation systems 1′, . . . , 1 ^(XIX), in the layers12′-12 ^(VI), in particular as outer corona protection, mostparticularly for such a high-voltage insulation system, the outer coronaprotection being composed electrically conductively in the form oflayers.

The high-voltage insulation system may be a simple system or a morecomplex system as in FIG. 20.

The invention is only explained on the basis of PTFE as an example of ahydrophobic material.

Preferably, the hydrophobic material or PTFE will already be composedelectrically conductively. The PTFE is then a composite material.

This preferably takes place during the production of the material bymeans of mixing in graphite in particular, by means of extrusion duringthe production, with fibers then preferably being produced. However,subsequent electrical coating of a woven fabric, a fiber, a laid scrimor a film is also possible.

The woven fabric is preferably formed from such fibers.

This woven fabric is preferably present in tape form and for theapplication is wound onto the surface to be insulated (see FIG. 20).

Preferably, therefore, the outer corona protection comprises fibers or awoven fabric of PTFE, with electrically conductive material, preferablygraphite, preferably also being present between the fabric-formingstructures to achieve the electrical conductivity.

Similarly, the tape (woven fabric, fiber, film, laid scrim) may beperforated.

The insulation according to FIGS. 1 to 19 preferably has for the outercorona protection a woven fabric of PTFE, this being structurallydesigned in such a way that the fabric has pores that can be infiltratedas above by the process described.

This yields the following advantages:

-   -   Good impregnatability, since it is a porous woven fabric and can        consequently be applied before the curing.    -   Unchanged resistance before and after the impregnation, since        the conductivity is attributable to fibers and not to particles        as in the case of OCP tape. (These have a different resistance        value in comparison with the initial value on account of the        polymer matrix enveloping the particles after the impregnation).

The objectives for OCP-G are:

-   -   simplified application/cost reduction    -   reduced layer thickness of the double OCP by a thinner        alternative

The approach for OCP-G is:

-   -   To reduce the layer thickness by using a separating layer, which        provides a defined mechanical decoupling without causing the        electrical resistance to change. This is intended to be        accomplished by replacing the double layer of laminated mica        with hydrophobic types of woven fabric. This may in particular        be a Teflon fabric. The structure is made up in the following        way:

An improvement is obtained according to the invention by the use ofelectrically conductive woven fabric 190 of PTFE, since this makes the“interweaving” of the outer corona protection tape 140 (FIG. 20)unnecessary, and as a result would make it possible to reduce the layerthickness and the production complexity (FIG. 20).

The structure according to the invention of an innovative outerpotential control for use in the GVPI process makes possible aninsulation system that corresponds in its properties to the currentstate of the art but has the benefits of:

-   -   establishing freedom from partial discharges after curing    -   comparable loss factors after carrying out thermal cycling tests        for accelerated thermomechanical loading    -   comparable electrical endurances under operational voltage        loading and with increased voltage loading    -   comparable electrical endurances under operational voltage        loading and with increased voltage loading after artificial        aging in different thermal cycles.

These investigations were carried out on generator winding bars with thefollowing design:

-   -   aluminum profiles with a length of about 1.5 m and dimensions of        1 cm×5 cm    -   number of layers of mica 10+1 layer of IPC for a nominal voltage        of 13.8 kV    -   number of generator winding bars per collective: 6.

In this case, a reduction of the layer thickness of the current OCP ofabout 450 μm to a value of about 100 μm was made possible.

1. An insulation system comprising: a metallic bar; a main insulationaround the bar; and at least one first layer of a first electricallyconductive, hydrophobic material around the main insulation andoptionally a second further layer of a different second electricallyconductive material directly on the main insulation, and optionally athird further outermost layer of an electrically conductive material,wherein the electrically conductive materials of the second and thirdfurther layers are different from the first electrically conductive,hydrophobic material.
 2. The insulation system as claimed in claim 1,wherein the main insulation is comprised of mica serving as awell-adhering, electrically conductive material.
 3. The insulationsystem as claimed in claim 1, wherein the material of the second furtherlayer is a well-adhering, electrically conductive material arrangeddirectly on the main insulation.
 4. The insulation system as claimed inclaim 1, wherein the first hydrophobic material is arranged directly onthe main insulation.
 5. The insulation system as claimed in claim 1,further comprising a fourth further layer between the first layer withthe hydrophobic material and the main insulation of a material ofwell-adhering, electrically conductive material, which is different fromthe first hydrophobic material.
 6. The insulation system as claimed inclaim 1, wherein the third outermost insulating layer is ofwell-adhering, electrically conductive material.
 7. An insulation systemcomprising: a metallic bar; a main insulation around the bar; and atleast one first layer of a first electrically conductive, hydrophobicmaterial around the main insulation and optionally a second furtherlayer of a different second electrically conductive material directly onthe main insulation and further comprising: a layer which consists ofelectrically conductive, hydrophobic material is the outermost layer. 8.The insulation system as claimed in claim 1, wherein the first layer andthe layer of electrically conductive, hydrophobic material includewell-adhering, electrically conductive material.
 9. The insulationsystem as claimed in claim 19, wherein the tapes are in a form ofwindings that partially overlap one another in a succession of windings.10. The insulation system as claimed in claim 19, wherein the tapes arein a form of a succession of windings, each winding having edges, andthe edges of successive windings of the tapes abut one another.
 11. Theinsulation system as claimed in claim 19, wherein the tapes which arearranged at a spacing from one another.
 12. The insulation system asclaimed in claim 7, which has the main insulation and only three of theinsulating layers.
 13. The insulation system as claimed in claim 7,which has the main insulation and only two of the insulating layers. 14.The insulation system as claimed in claim 7, which has the maininsulation and only and only one of the insulating layers.
 15. Theinsulation system as claimed in claim 7, which has the main insulationand only one of the layers of electrically conductive, hydrophobicmaterial.
 16. The insulation system as claimed in claim 1, furthercomprising PTFE as the electrically conductive, hydrophobic material.17. An outer corona protection, comprises an insulation system asclaimed in claim
 1. 18. An electrical machine, comprising a generator,which includes an insulation system as claimed in claim
 1. 19. Theinsulation system of claim 1, wherein the hydrophobic material is in atape form of one or more tapes wrapped around the main insulation.